Octagonal silica toroidal microcavity for controlled optical coupling

We fabricated polygonal silica toroidal microcavities to achieve stable mechanical coupling with an evanescent coupler such as a tapered fiber. The octagonal cavity was fabricated by using a combination of isotropic etching, anisotropic etching, and laser reflow. It offers both high and low coupling efficiencies with the cavity mode even when the coupler is in contact with the cavity, which makes the device more practically because of easy alignment. A numerical simulation showed that an octagonal silica toroidal microcavity had an optical quality factor of 8.8 × 10 ⁶.